Frame synchronization techniques

ABSTRACT

Frame synchronization techniques are described. In an implementation, a method implemented by a device includes using an objective function to form a list of values for a plurality of time trials, the time trials taken from a scan of a wireless signal having a plurality of channels. A single one of the values is selected for each of the plurality of channels to detect a preamble of a frame in the wireless signal. If the preamble is not detected as a result of the selecting, at least one additional value is chosen from the list for a respective channel to detect the preamble of the frame in the wireless signal.

RELATED APPLICATIONS

This application claims priority to U.S. Provisional Application Ser.No. 61/089,586, filed on Aug. 18, 2008, the disclosure of which isherein incorporated by reference in its entirety. This application isalso related to U.S. application Ser. No. 12/057,221, filed Mar. 27,2008.

BACKGROUND

A wide variety of techniques are usable to communicate wirelesslybetween devices. One such technique is referred to as WiMAX, which is anacronym for Worldwide Interoperability for Microwave Access and iscommonly used to refer to Institute of Electrical and ElectronicsEngineers (IEEE) 802.16 standards. WiMAX is a wireless broadbandtechnology that supports a variety of transmission modes, such as pointto multi-point (PMP) broadband wireless access.

WiMAX techniques communicate wirelessly through the use of frames. Inorder to detect a frame, a preamble is specified for the frame thatprovides a reference for frame synchronization, which framesynchronization is used to establish frame timing and initial symboltiming for the frame. The preamble employs a symbol structure toestablish fixed relationships among subcarriers of a signal and toindicate a start of a downlink frame. These fixed relationships areusable to minimize effects of distortions and interruptions, such as toadjust a timing offset, a frequency offset, transmitted signal power,and so on. In some instances, however, conventional techniques used forframe synchronization fail by detecting a false synchronization frame,interference in an upload/download gap, and so on.

SUMMARY

Frame synchronization techniques are described. In an implementation, amethod implemented by a device involves using an objective function toform a list of values for a plurality of time trials. The time trialsare taken from a scan of a wireless signal having a plurality ofchannels. A single one of the values is selected for each of theplurality of channels to detect a preamble of a frame in the wirelesssignal. If the preamble is not detected as a result of the selection, atleast one additional value is chosen from the list for a respectivechannel to detect the preamble of the frame in the wireless signal.

In an implementation, a mobile device includes an antenna and one ormore modules to perform frame synchronization. Frame synchronization isperformed by the one or more modules upon receiving a wireless signalhaving a plurality of channels via the antenna. At least two values areused that are computed using an objective function to attempt to detecta preamble of a frame in the wireless signal. Each of the at least twovalues corresponds to a single one of the channels. If the preamble isnot detected using the at least two values, at least one value computedusing the objective function for another one of the channels is used toattempt to detect the preamble of the frame.

In an implementation, a system comprises one or more modules configuredto compute a plurality of values using an objective function for a scanof a wireless signal in which each of the plurality of values iscomputed for a single one of a plurality of channels of the wirelesssignal. The plurality of values is iteratively used to detect a preambleof a frame in the wireless signal for frame synchronization.

This Summary is provided to introduce a selection of concepts in asimplified form that are further described below in the DetailedDescription. This Summary is not intended to identify key features oressential features of the claimed subject matter, nor is it intended tobe used as an aid in determining the scope of the claimed subjectmatter.

BRIEF DESCRIPTION OF THE DRAWINGS

The detailed description is described with reference to the accompanyingfigures. In the figures, the left-most digit(s) of a reference numberidentifies the figure in which the reference number first appears. Theuse of the same reference numbers in different instances in thedescription and the figures may indicate similar or identical items.

FIG. 1 is an illustration of an environment in an example implementationthat is operable to perform frame synchronization techniques.

FIG. 2 is an illustration of a system in an example implementationshowing a mobile station of FIG. 1 as evaluating data from an objectivefunction for use in detecting a preamble.

FIG. 3 is a flow diagram depicting a method in an example implementationin which a preamble is detected using a plurality of values computed fora single channel of a wireless signal having a plurality of channels.

FIG. 4 is a flow diagram depicting a method in an example implementationof a two-scan frame synchronization technique.

FIG. 5 is a flow diagram depicting a method in an example implementationin which a two-scan frame synchronization technique uses normalizedautocorrelation as an objective function.

FIG. 6 is an illustration of an example device configured as asystem-on-chip (SoC) that is operable to perform the framesynchronization techniques.

DETAILED DESCRIPTION

Example Environment

FIG. 1 is an illustration of an environment 100 in an exampleimplementation that is operable to perform frame synchronizationtechniques. The environment 100 may include a wide variety of devicesthat communicate wirelessly, examples of which include a base station102 and a mobile station 104 that are communicatively coupled via awireless network 106. Although the base station 102 and the mobilestation 104 are illustrated as examples, it should be readily apparentthat a wide variety of wireless devices may employ the techniquesdescribed herein, such as between mobile stations, through use of apoint to multi-point structure, and so on.

The base station 102 and the mobile station 104 are further illustratedas including respective communication modules 108, 110. Thecommunication modules 108, 110 are representative of functionality ofthe respective devices to communicate via the wireless network 106. Forexample, the communication modules 108, 110 are configurable to usetechniques such as Orthogonal Frequency Division Multiplexing (“OFDM”)or Orthogonal Frequency Division Multiple Access (“OFDMA”) to modulate asignal for wireless communication of data 112. In an implementation, themodulation is performed in accordance with WiMAX (IEEE 802.16) wirelesscommunication standards.

The data 112 is communicated through the use of frames, examples ofwhich are illustrated as an uplink frame 112 and a downlink frame 114.The uplink frame 112 specifies a frame for communicating data from themobile station 104 to the base station 102 over the wireless network106. The downlink frame 114 specifies a frame for communicating datafrom the base station 102 to the mobile station 104.

The download frame 114 further includes a preamble 116, which is used bya frame synchronization module 118 of the mobile station 104 to performframe synchronization. Frame synchronization is typically performedfirst as part of a signal acquisition procedure by the mobile station104 and involves identifying a start of the downlink frame 114. Forexample, the frame synchronization module 118 performs framesynchronization to determine timing and other characteristics of asignal transmitted by the base station 102 to the mobile station 104 viathe wireless network 106. The frame synchronization module 118 then usesthese characteristics to form a wireless communication channel betweenthe base station 102 and the mobile station 104. A variety of differenttechniques are usable to perform frame synchronization, examples ofwhich follow.

A conventional preamble signal structure contains data that describes anIDCell and segment. The IDCell and segment are used to identify whichbase station (e.g., tower) in which cell transmits the signal.Therefore, different preamble symbols are used from cell to cell andfrom segment to segment, and in an implementation each cell includesthree segments. Consequently, values and/or structure (e.g., patterns)of preamble symbols in the preamble 116 of the downlink frame 114 fromthe base station 102 are different from other preambles received by themobile station 104 from other base stations. Therefore, the base station102 (and more particularly data 112 communicated to and/or from the basestation) is uniquely identifiable from the other base stations.

Using these techniques, one of 114 different preamble symbol structurepatterns are available based on the base station IDCell and segment whengenerating a subchannel for a preamble symbol. To generate the preamble116, the base station 102 chooses one of the 114 preamble symbolstructure patterns based on the base station's IDCell number and segmentindex.

Individual subcarriers within the segment are also modified to reflectthis choice. For example, the subcarriers are modulated with the chosenpreamble symbol structure pattern using a Binary Phase Shift Keying(BPSK) format. Using this format, each segment uses a different set ofsubcarriers. The number of subcarriers used for each segment isgenerally equal to a length of the preamble sequence, which is a numberof symbols in the preamble 116.

Consequently, for conventional OFDMA signals the subcarrier set reflectsthe segment chosen by the base station 102. After the preamble symbolstructure pattern is chosen, an Inverse Fast Fourier Transform (IFFT) orreverse IFFT is performed to convert the signal from a frequency domaininto a time domain, and a cyclic prefix is added. The signal is thenwirelessly transmitted by the base station 102 over the wireless network106 to the mobile station 104.

Pilot subcarriers (e.g., control signals) are used to synchronize themobile station 104 with the base station 102 using phase, frequency,and/or timing considerations. The pilot subcarriers are modulated by thebase station 102 to reflect the preamble symbol structure pattern, withdifferent pilot subcarrier sets chosen depending on the segment assignedto the particular base station. Once these pilot subcarriers are knownby the mobile station 104, the pilot subcarriers are used for correctingmagnitude (power) and/or phase shift offsets (distortions) in subsequentsignals received by the mobile station 104) from the base station 102.

To aid in locating the preamble 116, the preamble 116 is differentiatedfrom a remainder of a frame structure of the downlink frame 114 using avariety of techniques. For example, power used to transmit the preamble116 is boosted above that of other symbols in the downlink frame 114that are outside of the preamble 116, e.g., eight times that overnon-preamble symbols, to 4 decibels, and so on. In another example,modulation of the preamble 116 is performed using BPSK while the rest ofthe downlink frame 114 is modulated using a different algorithm, such asQuadrature Phase Shift Keying (QPSK). In a further example, a subcarrierallocation of the preamble 116 is different from a subcarrier allocationof a remainder of the downlink frame 114. A variety of other examplesare also contemplated, such as peak-to-average power ratio and so on.

Thus, the strategy followed in this example involves identification ofone or more unique features of the preamble symbols (e.g., power,modulation, subcarrier allocation, and so on) such that the framesynchronization module 118 differentiates symbols in the preamble 116from other symbols in the downlink frame 114. To differentiate thesymbols, the frame synchronization module 118 employs an objectivefunction 120 with a trial of frame start as an argument. The objectivefunction 120 is constructed such that the function is optimized when acandidate that is a trial of frame start is the true frame start.Further discussion of an example objective function is found in relationto FIG. 5.

In a conventional technique, the value of the objective function iscomputed for each timing trial within a frame interval. A value takenfrom a single timing trial (e.g., a global optimum value) of a singlechannel is then selected as an estimate of a true frame start. Thesingle timing trial is the optimal value of the objective function 120from each of the timing trials for that single channel. Thus, in thisconventional technique, other values of the timing trials for the singlechannel are ignored and not used to determine the true frame start.However, in some instances the value of the objective function 120 forthe true frame start does not coincide with the global optimum valueamong each of the timing trials. Consequently, this conventionaltechnique for frame synchronization could become deadlocked in someinstances and thus fails to acquire the frame start.

Accordingly, the frame synchronization module 118 leverages the globaloptimum value, and in some instances also local optima values for theobjective function 120 in order to locate the true frame start of thedownlink frame 114. In this way, the frame synchronization module 118helps to detect the true frame start in instances that would haveresulted in frame synchronization deadlock using the above describedconventional technique alone.

FIG. 2 illustrates an example system 200 showing the mobile station 104as evaluating a plurality of time trials for frame synchronization. Themobile station 104 includes the communication module 110, which includesfunctionality of the frame synchronization module 118 and an objectivefunction 120. The objective function 120 is used to perform framesynchronization by determining a start of the downlink frame 114 throughdetection of the preamble 116.

The objective function 120 processes data describing a signal receivedfrom the base station 102 using normalized autocorrelation and arrivesat objective function data 204, which is illustrated through use of agraph in FIG. 2. Further discussion of normalized autocorrelation isdescribed in relation to the example methods section below.

The graph of the objective function data 204 specifies a plurality oftime trials as segments denoted as “T₀,” “T₁,” “T₂,” “T₃,” through “T₀”along the x-axis. The y-axis represents a relative magnitude ofrespective values output by the objective function 120 at thecorresponding times in response to the signal 202. In an implementation,the amount of time specified for each of the time trials is equal to orgreater than an amount of time specified for transmitting the downlinkframe 114, e.g., through one or more WiMAX standards.

As previously described, in some instances the value of the objectivefunction 120 for the true frame start is not be the global optimum value206 among each of the timing trials. However, of the remaining values inthe objective function data 204, the local optima values 208-212 have anincreased likelihood of being the true frame start when compared withother values of the objective function data 204. Therefore, in animplementation the frame synchronization module 118 maintains a list ofobjective function optima 214 that includes the global optimum value 206and local optima values 208-212. Thus, the frame synchronization module118 selects the global optimum value 206 and/or one of the local optimavalues 208-212 as candidates for detecting a true frame start, i.e., thestart of the downlink frame 114, for frame synchronization.

In an implementation, the frame synchronization module 118 employs atwo-scan frame synchronization technique in which the global optimumvalue 206 of an initial scan is first selected as a candidate. Shouldthe global optimum value 206 fail as an indicator of the true framestart, the frame synchronization module 118 then selects one of thelocal optima values 208-212 from a second scan as a candidate. Thus,deadlocks and failures that were encountered using conventionaltechniques are minimized and even eliminated. Further discussion ofthese and other frame synchronization techniques are described inrelation to the following methods.

Generally, any of the functions described herein can be implementedusing software, firmware, hardware (e.g., fixed logic circuitry), manualprocessing, or a combination of these implementations. The terms“module,” “functionality,” and “logic” as used herein generallyrepresent software, firmware, hardware, or a combination thereof. In thecase of a software implementation, the module, functionality, or logicrepresents program code that performs specified tasks when executed on aprocessor (e.g., CPU or CPUs). The program code can be stored in one ormore computer readable media, e.g., memory. The features of the framesynchronization techniques described below are platform-independent,meaning that the techniques may be implemented on a variety ofcommercial computing platforms having a variety of processors.

Example Methods

The following discussion describes frame synchronization techniques thatare implemented utilizing the previously described systems and devices,as well as other systems and devices. Aspects of each of the methods areimplemented in hardware, firmware, software, or a combination thereof.The methods are shown as a set of blocks that specify operationsperformed by one or more devices and are not necessarily limited to theorders shown for performing the operations by the respective blocks. Inportions of the following discussion, reference will be made to theenvironment 100 of FIG. 1 and the system 200 of FIG. 2.

FIG. 3 depicts a method 300 of detecting a preamble using a plurality ofvalues computed for a single channel of a wireless signal having aplurality of channels. A wireless signal is received by a device via anantenna that has a plurality of channels (block 302). For example, themobile station 104 receives the signal 202 wirelessly from the basestation 102 via the antenna illustrated in FIG. 1.

At least two values are computed using an objective function such as anormalized autocorrelation function. The at least two values are used toattempt to detect a preamble of a frame in a wireless signal in whicheach of the values corresponds to a single one of the channels (block304). Continuing with the previous example, the frame synchronizationmodule 118 of the mobile station 104 uses the objective function 120 tocompute objective function data 204. The objective function data 204 ofFIG. 2 is segmented across a plurality of time trials such that eachtime trial has a respective local optima value, e.g., a maximum valuefor the objective function data for that time trial. The local optimavalues in this example correspond to a single channel of a plurality ofchannels included in the signal 202, such as when the signal complieswith one or more IEEE 802.16 standards.

A determination is then made as to whether a preamble was detected(decision block 306) using the values. The at least two values areprovided in succession (e.g., iteratively) for further processing todetect the preamble and therefore the true frame start as previouslydescribed. If the preamble is detected (“yes” from decision block 306),the frames are synchronized (block 308). The frame synchronization isthen used to form a wireless communication channel between the basestation 102 and the mobile station 104.

If the preamble is not detected (“no” from decision block 306), at leastone value computed using the objective function for another one of thechannels is used to attempt to detect the preamble of the frame (block310). As before, the determination is then made as to whether thepreamble is detected (decision block 312), and if so (“yes” fromdecision block 312) the frames are synchronized (block 308). If thepreamble is not detected (“no” from decision block 312), another valuecomputed using the objective function for the other one of the channelsis used to detect the preamble of the frame (block 314).

The at least two values of block 304 are local optima values forrespective time trials that correspond to a first channel. The othervalues computed by the objective function for blocks 310 and 314 arealso local optima values. In this instance, however, the local optimavalues correspond to a second channel that is different than the firstchannel. In an implementation, the first and second channels aresub-channels of the signal 202 that are formed in compliance with one ormore OFDM techniques such as IEEE 802.16. Therefore, in this method 300the frame synchronization module 118 uses a plurality of local optimavalues for a single channel of the signal 202 to detect a preamblebefore using additional local optima values that correspond toadditional channels of the signal 202. In other words, multiplecandidates (values) of a single channel are used for framesynchronization before another candidate of another channel is used.Thus, this technique is referred to later in the following discussion asa multiple candidate technique. The multiple candidate technique may beincorporated with a single candidate technique (e.g., one candidate perchannel) that was previously described to implement a two-scan framesynchronization technique, an example of which is described in relationto the following figure.

FIG. 4 depicts a method 400 in an example implementation of a two-scanframe synchronization technique. An objective function is computed foreach of a plurality of time trials of an initial scan of a wirelesssignal to generate objective function data (block 402). For example, thesignal 202 is received at an antenna of the mobile station 104 during asignal acquisition process.

A list of local optima values is formed from data computed using theobjective function for respective time trials (block 404). For example,the objective function data 204 as previously described includes aplurality of local optima values which includes a global optimum value206 (as it is a local optima value of time trial T₂) as well as localoptima values 208-212 of other time trials. These local optima valuesare collected to form a list of objective function optima 214 that ismaintained by the mobile station 104.

For the initial scan of the wireless signal, a single local optimumvalue (e.g., a global optimum value 206) is selected from the list foreach channel of the wireless signal to perform frame synchronization(block 406). In an implementation, the frame synchronization module 118selects a first global optimum value that corresponds to a first channelof the signal 202. If the preamble cannot be detected using the firstglobal optimum value and thus signal acquisition fails using the firstglobal optimum value, a second global optimum value that corresponds toa second channel of the signal 202 is chosen. Therefore, this techniquedescribes a single candidate per channel analysis that is performed forthe initial scan using global optima values to initially detect apreamble 116.

However, if the frame synchronization fails, an addition scan of thewireless signal is performed (block 408). As before, the objectivefunction is computed for each of a plurality of time trials of theadditional scan to generate objective function data (block 410). A listof local optima values is also formed from data computed using theobjective function for respective time trials in the additional scan(block 412). This list may be the same as or different from the listformed at block 404.

For the additional scan of the wireless signal, a single global optimumvalue is selected from the list for each channel of the wireless signalto perform frame synchronization (block 414). Thus, functions performedfor the additional scan of block 410-414 in this example mimic functionsperformed for the initial scan of blocks 402-404.

If the frame synchronization fails, however, at least one additionallocal optimum value is selected from the list to perform framesynchronization such that a plurality of the local optimum values thatcorrespond to a single channel are used for frame synchronization (block416). In an implementation, these techniques employ the method 300described in relation to FIG. 3 that details use of a plurality of localoptima values for a single channel of a wireless signal to detect apreamble before using additional local optima values.

Therefore, in the described two-scan frame synchronization technique aone channel/one candidate technique (e.g., using the global optimavalue) is first used to detect a preamble in the initial scan. If thistechnique is not successful, a one channel/multiple candidate techniqueis employed to detect the preamble. Thus, the two-scan framesynchronization technique leverages the increased accuracy of themultiple candidate technique and the efficiency of the one candidatetechnique. Although multiple scans were described in relation to method400, it should be readily apparent that the techniques may employ asingle scan, e.g., formation of a single list to perform thesingle/multiple candidate techniques.

FIG. 5 depicts a method 500 in an example implementation in which atwo-scan frame synchronization technique uses normalized autocorrelationas an objective function. A front-end gain, a normalizedautocorrelation, and an unnormalized autocorrelation are computed (block502). The front-end gain is computed by measuring a power of thepreamble 116 as compared to a remainder of a downlink frame 114.

The normalized correlation is computed using the following expression.This expression leverages a unique subcarrier allocation pattern with apreamble symbol to distinguish preamble symbols from other symbols inthe frame. For example, in a frequency domain each third subcarrier isused to modulate the preamble sequence. In a time-domain, the signal isrepeated three times. Thus, these features may be used to locate an OFDMpreamble symbol without performing a FFT. Accordingly, the followingobjective function to compute a normalized autocorrelation C(k) isconstructed to use this unique signal repetition pattern within apreamble symbol to aid in detecting a preamble:

${{C(k)} = \frac{{{\sum\limits_{l = 0}^{{2*{{round}{({N/3})}}} - 1}\;{z_{k - l - {{round}{({N/3})}}}z_{k - l}^{*}}}}^{2}}{\left\lbrack {{\frac{1}{2}{\sum\limits_{l = 0}^{{2*{{round}{({N/3})}}} - 1}\;{z_{k - l - {{round}{({N/3})}}}}^{2}}} + {z_{k - l}}^{2}} \right\rbrack^{2}}},{k = T_{0}},\ldots\mspace{14mu},{T_{0} + W - 1}$In the above expression, the following variables and expressions aredefined as follows:

-   -   yk is a k-th received time-domain Nyquist sample;    -   z_(k) is a k-th received differential time-domain sample and is        equal to y_(k)−y_(k-1);    -   N is FFT size and not a multiple of 3;    -   T₀ is a start time of frame synchronization;    -   W is a frame synchronization observation interval; and    -   C(k) is the objective function, which performs a normalized        autocorrelation of a received signal.        Further, the estimate of the true frame start “τ” (and the        preamble) is expressed as follows:

$\tau = {\arg\mspace{11mu}{\max\limits_{k \in \Omega}{C(k)}}}$Ω = {k:C(k) ≥ Threshld, ∀k}Thus, as shown in the above expression the estimate of the frame isgreater than a predefined threshold as previously described.

The unnormalized autocorrelation A(k) is computed using a numerator ofthe normalized autocorrelation expression C(k) above, which is expressedas follows:

${A(k)} = {{\sum\limits_{l = 0}^{{2*{{round}{({N/3})}}} - 1}\;{z_{k - l - {{round}{({N/3})}}}z_{k - l}^{*}}}}^{2}$

A current time index is checked to determine if the current time indexis within a neighborhood of a local optimum value (decision block 504).If not (“no” from decision block 504), the method 500 returns to block502. If so (“yes” from decision block 504), the method 500 proceeds toblock 506. A variety of different techniques may be used to determine ifthe current time index is within the neighborhood of the local optimumvalue. For example, the frame synchronization module 118 is configurableto identify entry into the neighborhood of a local optimum value if theC(k) is continuously greater than the threshold for a predeterminedamount of time. The frame synchronization module 118 is alsoconfigurable to identify an exit from the neighborhood of the localoptimum value if the C(k) is continuously less than the threshold for apredetermined amount of time.

In another example, the frame synchronization module 118 is configuredto identify entry into the neighborhood of a local optimum value if C(k)is greater than a threshold and a timer to record local optimum valuetiming is 0. In this example, the frame synchronization module 118identifies an exit from the neighborhood of a local optimum value if thetimer to record the local optimum value timing has expired. The amountof time used by the timer (i.e., the time out duration) is equal to aduration T of a single symbol.

A determination is then made as to whether the normalizedautocorrelation value is greater than a current local optimum value(decision block 506). If not (“no” from decision block 506), the method500 returns to block 502. If so (“yes” from decision block 506), thevalues are updated (block 508). The current local peak value is updatedusing the normalized autocorrelation value such that max_C=C(k). Othervalues are also updated, which includes the unnormalized autocorrelationvalue (max_A=A(k)), the front-end gain (max_G=G(k)), and the time(max_T=k).

At an end of a coarse frame synchronization observation window, onelocal optimal value that is optimal when compared to other local optimalvalues (i.e., the global optimal value) is selected as a candidate for atrue frame start for further processing to detect the preamble (block510). The coarse frame synchronization observation window may be set toan amount of time to perform a scan, e.g., to perform a desired numberof time trials.

At the end of this time, a determination is made as to whether there arevalues having a max_C that is greater than a high threshold, whichindicates that the system (e.g., the base station 102 and the mobilestation 104) operates at a high signal-to-noise ratio (SNR). If so,among each of the entries having a max_C greater than thehigh-threshold, a max_A/max_G² is found among them and the correspondingmax_T is selected as the frame start. In not, a maximum max_C is foundand the corresponding max_T is selected as the frame start.

If the further processing indicates an acquisition failure, then a timeindex local peak value is tried for each local optimum value as a framestart (block 512) until the preamble is detected, e.g., in a descendingorder of local optima values. The time index values max_T for each ofthe local optima values are used successively for further processing asdescribed above to detect the preamble 116. In an implementation, blocks502-510 are performed for an initial scan while blocks 502-512 areperformed for the additional scan. Thus, this method 500 employs thetwo-scan frame synchronization technique described above to leverage theincreased accuracy of the multiple candidate technique with theefficiency of the one candidate technique. However, a variety of otherexamples are also contemplated, e.g., a single scan using multiplecandidates, multiple scans in which the initial scan uses the singlecandidate techniques and the additional scan uses both the single scanand the multiple scan techniques, and so on.

Example Device

FIG. 6 illustrates an example System-on-Chip (SoC) 600, which canimplement various embodiments of the frame synchronization techniques ina variety of wireless devices. An SoC may be implemented in a fixed ormobile device (e.g., mobile station 104), a media device, computerdevice, television set-top box, video processing and/or renderingdevice, appliance device, gaming device, electronic device, vehicle,workstation, and/or in any other type of device that may communicatewirelessly in a local or personal area network. Examples of some ofthese are shown in FIGS. 1 and 2.

SoC 600 can be integrated with electronic circuitry, a microprocessor,memory, input-output (I/O) logic control, communication interfaces andcomponents, other hardware, firmware, and/or software needed to run anentire device. SoC 600 can also include an integrated data bus (notshown) that couples the various components of the SoC for datacommunication between the components. A device that includes SoC 600 canalso be implemented with many combinations of differing components.

In this example, SoC 600 includes various components such as aninput-output (I/O) logic control 602 (e.g., to include electroniccircuitry) and a microprocessor 604 (e.g., any of a microcontroller ordigital signal processor). SoC 600 also includes a memory 606, which canbe any type of random access memory (RAM), a low-latency nonvolatilememory (e.g., flash memory), read only memory (ROM), and/or othersuitable electronic data storage. SoC 600 can also include variousfirmware and/or software, such as an operating system 608, which can becomputer-executable instructions maintained by memory 606 and executedby microprocessor 604. SoC 600 can also include other variouscommunication interfaces and components, wireless LAN (WLAN) or PAN(WPAN) components, other hardware, firmware, and/or software.

SoC 600 may also include a wireless transmitter 610 and wirelessreceiver 612 that may be communicatively coupled to an antenna. Examplesof these various components, functions, and/or entities, and theircorresponding functionality, are described with reference to therespective components of the examples of FIGS. 1 and 2.

The frame synchronization module 120 in SoC 600, either independently orin combination with other entities, can be implemented ascomputer-executable instructions maintained by memory 606 and executedby microprocessor 604 to implement various embodiments and/or featuresof the tools. In another example, the frame synchronization module 120may also be provided integral with other entities of the SoC, such asintegrated with one or both of wireless transmitter 610, wirelessreceiver 612, I/O logic control 602, and so on. Alternatively oradditionally, the frame synchronization module 120 and the othercomponents can be implemented as hardware (e.g., fixed logic circuitry),firmware, or any combination thereof that is implemented in connectionwith the I/O logic control 602 and/or other signal processing andcontrol circuits of SoC 600.

Although the invention has been described in language specific tostructural features and/or methodological acts, it is to be understoodthat the invention defined in the appended claims is not necessarilylimited to the specific features or acts described. Rather, the specificfeatures and acts are disclosed as example forms of implementing theclaimed invention.

1. A method implemented by a device, the method comprising: using anobjective function to form a list of values for a plurality of timetrials, the time trials taken from a scan of a wireless signal having aplurality of channels; selecting a single one of the values for each ofthe plurality of channels respectively to detect a preamble of a framein the wireless signal, the preamble of the frame comprising a firstOrthogonal Frequency Division Multiple Access (OFDMA) symbol of theframe, the first OFDMA symbol generated based on a segment index and anidentifier of a base station that transmits the wireless signal; and ifthe preamble is not detected as a result of the selecting, choosing atleast one additional value from the list for one of the plurality ofchannels to detect the preamble of the frame in the wireless signal. 2.A method as described in claim 1, wherein the choosing is performed suchthat if the preamble is not detected after the at least one additionalvalue from the list that corresponds to the one of the plurality ofchannels is chosen, one or more values for another one of the pluralityof channels are chosen to detect the preamble.
 3. A method as describedin claim 1, wherein the selecting and the choosing are performed suchthat a plurality of the values for a single one of the plurality ofchannels are used by the device to detect the preamble.
 4. A method asdescribed in claim 1, wherein the single one of the values used for theselecting is a global optimum value.
 5. A method as described in claim4, wherein the at least one additional value used in the choosing is alocal optimum value.
 6. A method as described in claim 1, wherein theobjective function is used to compute a normalized autocorrelation. 7.The method of claim 1, wherein the values included in the list are abovea predefined threshold.
 8. A method as described in claim 1, furthercomprising: computing an initial list of values using the objectivefunction for a plurality of time trials of an initial scan of thewireless signal; using a single one of the values from the initial listfor each of the plurality of channels to detect the preamble; and if thepreamble is not detected for the initial scan as a result of the using,performing the scan that serves as a basis to form the list of valuesfor the plurality of time trials.
 9. A method as described in claim 1,wherein the device is a mobile station.
 10. A method as described inclaim 1, wherein the frame is a downlink frame in compliance with anInstitute of Electrical and Electronics Engineers (IEEE) 802.16standard.
 11. A mobile device comprising: an antenna; and one or moremodules to perform frame synchronization by: receiving a wireless signalhaving a plurality of channels via the antenna; using at least twovalues computed using an objective function to attempt to detect apreamble of a frame in the wireless signal in which each of the at leasttwo values corresponds to a single one of the plurality of channels, thepreamble of the frame comprising a first Orthogonal Frequency DivisionMultiple Access (OFDMA) symbol of the frame, the first OFDMA symbolgenerated based on a segment index and an identifier of a base stationthat transmits the wireless signal; and if the preamble is not detectedusing the at least two values for the single one of the plurality ofchannels, using at least one value computed using the objective functionfor another one of the plurality of channels to attempt to detect thepreamble of the frame.
 12. A mobile device as described in claim 11,wherein the one or more modules are configured to use the at least twovalues successively to attempt to detect the preamble of the frame. 13.A mobile device as described in claim 11, wherein the one or moremodules are further configured to use another value computed using theobjective function for the other one of the plurality of channels todetect the preamble of the frame if the preamble is not detected usingthe at least one value for the other one of the plurality of channels.14. A mobile device as described in claim 11, wherein the frame is adownlink frame in compliance with an Institute of Electrical andElectronics Engineers (IEEE) 802.16 standard.
 15. A mobile device asdescribed in claim 11, wherein the objective function is used to computea normalized autocorrelation from data describing the wireless signal.16. One or more computer-readable memory devices embodyingcomputer-executable instructions that, when executed by a processor,implement a frame synchronization module configured to: compute aplurality of values using an objective function, the plurality of valuesto analyze a scan of a wireless signal having a plurality of channels;use two or more of the plurality of values to attempt to detect apreamble of a frame in the wireless signal, the two or more valuescorresponding to a single one of the plurality of channels, the preambleof the frame comprising a first Orthogonal Frequency Division MultipleAccess (OFDMA) symbol of the frame, the first OFDMA symbol generatedbased on a segment index and an identifier of a base station thattransmits the wireless signal; and if the preamble is not detected usingthe two or more values for the single one of the plurality of channels,use another value computed using the objective function for another oneof the plurality of channels to attempt to detect the preamble of theframe.
 17. The one or more computer-readable readable memory devices asdescribed in claim 16, wherein the objective function is configured foruse in computing a normalized autocorrelation of the wireless signal.18. The one or more computer-readable readable memory devices asdescribed in claim 16, wherein the frame synchronization module isfurther configured to: compute another plurality of values using theobjective function, the other plurality of values to analyze the scan ofthe wireless signal, wherein each of the other plurality of valuescorresponds to another one of the plurality of channels that isdifferent than the single one of the plurality of channels; anditeratively use the other plurality of values to detect the preamble ofthe frame.
 19. The one or more computer-readable readable memory devicesas described in claim 16, wherein the one or more computer-readablememory devices are associated with or embodied as part of a system on achip (SoC).